Plastic lenses have rapidly come into wise use as lens materials for example, pickup lenses used for devices for spectacles, cameras, optical recording and reproduction instead of glass lenses in view of lightweight, impact resistance, Tintability(Dyeability) and the like. So, radical-polymerized polymer of diethylene glycol bis(allylcarbonate) (hereinafter, D.A.C.) polycarbonate (PC), polymethyl (meth)acrylate (PMMA) and the like have been used for plastic lenses. These plastic lenses have a drawback in that they might be easily scratched as compared to glasses. As one of measures to handle such a drawback, there was mentioned of a method for curing a multifunctional (meth)acrylate with ultraviolet rays (UV), thus forming a tight and hard layer (hard coatings or Abrasion-resistant coatings) on the surface of a lens.
On the other hand, in order to reduce the thickness of a lens, resins having much higher refractive index have been required instead of resins such as D.A.C., PC, PMMA and the like having the refractive index of around nd=1.49 to 1.58. There have been proposed a resin (around nd=1.60 to 1.67) which was obtained by forming a thiourethane bond by thermo-polymerization of a thiol compound and isocyanate compound in JP97-110956A, and a resin (nd=1.70 or more) which was obtained by forming an epithiosulfide bond by ring opening thermo-polymerization of a thio epoxy compound in JPO2-194083A.
Accompanied with diversity in plastic lenses, especially high refractive index, a demand for hard coatings has been diversified. In addition to characteristics requiring sufficient scratch resistivity and adherence to a lens, recently, it has been strongly required that no interference fringe was generated between the lens surface and hard coatings (refractive indexes of both materials adjusted).
These characteristics for adjusting the refractive index of a base material including an optical material are not only required for hard coatings of a lens, but strongly required for a wide variety of fields ranging to surface decoration of resin materials, metal materials, ceramic materials, glass materials and the like or adhesive agents, in view of anti-reflection for displays, surface protection for optical recording media aesthetically.
However, it is currently difficult to realize hard coatings that satisfy other requirement characteristics (scratch resistivity, adherence and the like) and in which the refractive index can be adjusted and especially higher refractive index can be obtained as well.
In JP96-179123A, there has been described a method of curing a composition comprising multifunctional acrylate and a kind of ultrafine inorganic oxide particles having high refractive index selected from antimonous oxide, tin oxide, indium-tin mixed oxide, cerium oxide, titanium oxide with ultraviolet rays.
However, as the refractive index of an aliphatic (meth)acrylate such as pentaerythritol triacrylate described in the document or the like is 1.5 or less by nature, in order to obtain high refractive index of more than 1.6 and more than 1.7, a lot of ultrafine inorganic oxide particles having high refractive index should be contained. As a result, a coating layer becomes weakened. Furthermore, when a composition having these aliphatic (meth)acrylate compounds as main components is used as hard coatings for lenses, as adherence to a resin having the aforementioned thiourethane bond or epithiosulfide bond is not sufficient, it can not be used.
Also, a method (sol-gel method) of forming hard coatings by thermal-curing of a silane coupling agent as a main component has been widely used, in which scratch resistivity was extremely high with certainty, and adherence to a resin having a thio urethane bond or epithiosulfide bond was sufficient as well. This method, however, had drawbacks in that heating conditions such as high temperature and long time were required for forming hard coatings and storage stability of a solution was usually within 1 month.
As a method to form high refractive index layer (film) on the surface of a resin or glass, there has been a physical method to form a layer such as titanium oxide, zirconium oxide and the like using vacuum evaporation, sputtering or the like. However, this method has problems in productivity in view of film production speed or the like, and allows a thin layer of about several nms, but it is practically difficult to form a thick layer having about several μms.